Seventh chords are constructed using the four odd-numbered notes of a seven-note scale (with exceptions), or by moving up in skips or thirds from any note within a seven-note scale (as in a harmonized scale).
The quality of the chord is determined by its comparison to a paralell major scale.
If it matches the first, third, fifth and seventh note, it is a major-seventh chord [ maj7, mj7,
7 ].
Alterations from this chord are described in chord formulas, which are used to create chord symbols.